Wear resistant alloy

ABSTRACT

In order to provide a material of low cost that is suitable to produce parts or coatings having a high wear and also high chemical resistance, an alloy is proposed comprising 13 to 16 percent by weight nickel (Ni), 13.5 to 16.5 percent by weight of chromium (Cr), 0.5 to 3 percent by weight of molybdenum (Mo), 3.5 to 4.5 percent by weight of silicon (Si), 3.5 to 4 percent by weight of boron (B) and 1.5 to 2.1 percent by weight of carbon (C), balance iron (Fe).

DETAILED DESCRIPTION

The invention relates to a material comprising an iron based alloycontaining C, B, Cr, Ni, Si and Mo.

The material or alloy may be used for producing formed products, castedproducts, coatings, parts, coated parts, wires, electrodes, powders andpowder mixtures.

PRIOR ART

There is a need in industry for an alloy material which has excellentresistance agains wear and corrosion and a low cost.

The use of nickel-based alloys with additions of chromium and molybdenumto give protection from wear and corrosion has long been known. Suchalloys are disclosed for example in the U.S. Pat. Nos. 6,027,583 A,6,187,115 A and 6,322,857 A.

EP 1 788 104 A1 discloses a material for producing parts or coatingsadapted for high wear and friction-intensive applications. The materialcomprises a nickel based alloy with the addition of hard particles suchas WC.

The elements Ni and W are expensive and alternatives are sought.

Iron-based self-fluxing alloys are an alternative group of lower costmaterials and many materials have been found that exhibit reasonablewear resistance.

Such an iron-based alloy is known from DE 197 33 306 C1. It discloses aniron-based thermal coating material. The alloy is used as additivematerial, in the form of a mixture, a gas atomized alloy, anagglomerated metal powder, a core-filled wire, a core-filled strip, asintered strip or a cast sheathed rod electrode and used for thermalcoating of components exposed to friction. A preferred composition ofthe alloy for applying a low friction and low wear layer for a slidingcomponent pairing with good fatigue and impact resistance is as follows(by weight): 20-25% Mn, 13-20% Cr, 0.1-2% Ni, 3-6% W, 0.1-0.15% C,1.5-2.5% B, balance Fe. Another preferred composition of the alloy forapplying a low friction layer with high abrasion resistance and higherthermal loading capacity is as follows (by weight): 18-25% Mn, 13-25%Cr, 0.1-2% Ni, 3-5% W, 0.1-0.15% C, 4-6% B, balance Fe.

DE 199 01 170 A1 discloses another iron alloy with high carbon, boron,vanadium, chromium, molybdenum and nickel contents. The followingcomposition is proposed (by weight): 2.0-4.0% C, 2.0-4.5% B, 0.5-3.5%Si, 6.0-15.0% Cr, 1.5-7.5% Mo, 6.0-14.0% V, 0-3.0% W, 0-1.5% Mn, 0-2.0%Cu, 2.0-7.0% Ni, balance Fe and impurities. The alloy is used forinternal hard facing of metal cylinders by centrifugal casting or hotisostatic pressing.

CA 2 416 950 A1 discloses a material for the manufacture of parts andtools for use at elevated temperature, comprising an iron-based alloycomprising C, Si, Mn, Cr, Ni and N in certain concentrations. The alloyis cold formed to a hardness of at least 230 HB.

However, there remain two problems with such Fe-based alloys. First, thewear resistance of these Fe-based alloys is still inferior to Ni-basedalloys with WC. To get close to those properties, the base alloy mustuse expensive alloying elements such as W, Nb or add large quantities ofWC particles. These alloying elements increase the price and make thematerial very hard (more than 65 HRC), which poses additional processingand application problems with cracking. Secondly, the Fe-based materialsdo not have a good corrosion resistance, like that of Ni based alloys,particularly in mixed corrosion environments.

OBJECT OF THE INVENTION

It is therefore an object of the invention to provide an alternativematerial of lower cost that is suitable to produce parts or coatingshaving a high wear and also high chemical resistance.

The object is achieved by a material comprising an alloy containing 13to 16 percent by weight nickel (Ni), 13.5 to 16.5 percent by weight ofchromium (Cr), 0.5 to 3 percent by weight of molybdenum (Mo), 3.5 to 4.5percent by weight of silicon (Si), 3.5 to 4 percent by weight of boron(B), 1.5 to 2.1 percent by weight of carbon (C) and 0.2 to 0.5 percentby weight of copper (Cu), balance iron (Fe).

It was found that such iron based alloys with C, B, Cr, Ni, Si and Moexhibit high wear and surprisingly high chemical resistance.

The material comprises an iron based alloy with the further componentsC, B, Cr, Ni, Si and Mo. The material includes the pure alloy andcoatings with a composition of the alloy.

The alloy contains only C, B, Cr, Ni, Si and Mo as major componentsbesides the main component Fe. Generally the alloy contains traces orminor amounts of other elements, which are generally common impurities.Less preferred, the alloy may contain other elements in concentrations,which do not alter its chemical behavior significantly. Such optionaladditives are named accompanying elements.

The alloy is useful for producing either coatings on a metal substrateor for producing formed products, casted products, coatings, parts,coated parts, wires, electrodes or powders.

In general the alloy consists of 13 to 16 percent by weight (wt.−%)nickel (Ni), 13.5 to 16.5 percent by weight of chromium (Cr), 0.5 to 3percent by weight of molybdenum (Mo), 3.5 to 4.5 percent by weight ofsilicon (Si), 3.5 to 4 percent by weight of boron (B) and 1.5 to 2.1percent by weight of carbon (C), balance iron (Fe) and possibleimpurities.

Impurities are normally present and are generally unavoidable. Thecontent of impurities in the alloy is generally less than 1 percent byweight, preferably less than 0.5 percent by weight and most preferredless than 0.2 percent by weight. All weight percentages mentioned arebased on the weight of the total composition, which is 100 percent byweight. All numerical values are approximate values.

In a less preferred alternative the alloy may contain one or moreaccompanying elements. The content of an accompanying element in thealloy is generally less than 3 percent by weight, preferably less than 2percent by weight and most preferred less than 1 percent by weight. Thewhole content of accompanying elements in the alloy is generally lessthan 5 percent by weight, preferably less than 3 percent by weight andmost preferred less than 2 percent by weight.

A preferred composition of the alloy is 13 to 14 percent by weight ofnickel (Ni), 14 to 16 percent by weight of chromium (Cr), 1 to 3 percentby weight of molybdenum (Mo), 3.5 to 4.5 percent by weight of silicon(Si), 3.5 to 4 percent by weight of boron (B), 1.8 to 2.1 percent byweight of carbon (C) and 0.2 to 0.5 percent by weight of copper (Cu),balance iron (Fe) and possible impurities.

The alloy has an unusual good corrosion resistance in mixed corrosionconditions where most Ni-based or Fe-based wear resistant materials donot satisfy. It is remarkable that the Fe-based alloy contains noaddition of other hard particles to increase its hardness, such asTungsten Carbide (WC).

Generally the alloys have a hardness in the ränge of 35 HRC to 60 HRC,particularly in the range of 55 HRC to 60 HRC, typically around 58 HRC,which is unusually low for such a wear resistant material. It gives anadvantage in processing and operation as it makes the alloy lesssensitive to cracking.

Here, the unit “HR” represents the so called “Rockwell hardness”. Thereare several Rockwell scales for different ranges of hardness. The mostcommon are the B scale (HRB), which is appropriate for soft metals, andthe C scale (HRC) for hard metals. The method for measuring hardnessaccording to Rockwell is specified in DIN EN ISO 6508—ASTM E-18.Rockwell hardness numbers are not proportional to Vickers hardnessreadings, but there exist conversion tables, according to which theabove range of 35 to 60 HRC is corresponding a Vickers hardness ofbetween 345 and 780 HV/10.

The alloys generally have a melting point in the range of 1.000 to1.150° C., typically around 1080° C. This a very low melting temperaturefor such an alloy with these properties, which reduces costs inprocessing and gives application advantages.

The alloy is produced in the conventional manner by melting of thecomponents or blending of powders or compounds.

The alloy can be cast to products of any shape.

The alloy is used for the production of parts or coatings on parts,which are generally metal substrates or metal parts, especially made ofsteel. Metal parts are e.g. rotors, sleeves, bearings, screws, blades,etc.

The material, in particular the alloy, is preferably used for theproduction of wires, filling wires, bands, strand-shaped products,electrodes, powders, pastes, slurries, or cast bar material, which areused e.g. for casting, welding, plasma transferred arc welding (PTA),plasma powder build-up welding or arc welding, brazing, flame spraying,in particular high-speed flame spraying (HVOF), sinter fusing andsimilar processes.

The invention also comprises a process for applying a material accordingto the invention for the production of coatings with a high level ofresistance to corrosion and wear on a workpiece by a thermal coatingprocess, in which the coating material in powder form is alloyed andatomized from the melt or agglomerated from various alloyed andnon-alloyed metal powders.

The coatings or protective layers of the alloy on parts, in particularmetal parts, are produced preferably by conventional methods of applyinga powder by pouring, casting, dipping, spraying, spinning followed by athermal fusion treatment or by thermal methods like flame spraying, andpreferably by high velocity flame spraying (HVOF), or by plasmatransferred are welding. Such coating methods are described, forexample, in U.S. Pat. No. 6,187,115 A and U.S. Pat. No. 6,322,857 A,which can be applied analogously and which are incorporated byreference.

Such coatings can be produced as mentioned above in the thermalprocesses by using materials containing the alloy, like powders, wires,electrodes or other conventional forms, or by applying two or morematerials, which deviate in the composition from the resulting finalalloy, where the materials are separate or mixed, e.g. differentelectrodes or mixed powders, resulting in a coating with the compositionof the alloy.

Such coatings or protective layers serve to give protection from wearand corrosion in the chemical industry, the pharmaceutical industry, thepaper industry, the glass industry, power industry, cement industry,waste and recycling, pulp and paper industry and the plastics-processingindustry. Coated parts are also used advantageously for oil and gasexploration applications.

Generally the coating has a thickness in the range of 0.1 to 20 mm,preferably 1 to 10 mm.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention shall now be explained in more detail with reference to anembodiment and a drawing which shows in detail in FIG. 1 a diagram onthe degree of volume loss in a standardized abrasion testing (ASTM G65)in dependence upon the alloy composition,

FIG. 2 a diagram on the degree of weight loss in a standardizedcorrosion test in contact with HCl in dependence upon the Ni content ofthe X5 alloy; and

FIG. 3 a diagram on the degree of weight loss in a standardizedcorrosion test in contact with HNO₃ in dependence upon the Ni content ofthe X5 alloy.

Example 1 Sample X5

A series of alloys is prepared by the fusion of metal elements andcompounds into a melt and producing two powders which are given in table1 below:

TABLE 1 Fe C Si Cr Ni Mo B Powder 3.7 0.26 4.58 16.4 59.76 12.9 2.87 APowder 71.47 2.03 3.12 14.01 5.62 0 3.59 B

The Powder B (which is a Fe-based alloy) was blended with varying wt %of Powder A (which is a Ni based wear resistant alloy which is alsodesignated by No. “53606”) and then fused at 1.080 C. It was found thatthere was an optimal % of powder A for wear and corrosion results thatlay between 10 and 40 weight % and that best results were obtained with15% of Powder A mixed with Powder B

This illustrated in FIG. 1. The 3 curves are wear rate data pointsobtained from the same fused mixtures but tested with the ASTM G65method at three independent test series (different times and places).The volume loss is plotted on the y-axis in [mm³] in dependence of thecontent of the Powder A in [wt %]. For all three test series acharacteristical low volume loss and therefore best wear resistance wereobtained with about 15% of Powder A mixed with Powder B.

In the following this 15% mixture of Powder A in Powder B alloy iscalled “X5”. “X5” is a Fe-based alloy containing no addition of otherhard particles to increase its hardness, such as Tungsten Carbide (WC).The following table 2 shows the composition of the X5 alloy incomparison with an Fe-based alloy as it is disclosed in DE 199 01 170A1. It is obvious that the Ni-content of the X5-alloy is higher and itsV-content is lower (namely zero) and the carbon and chrome levels arealso different.

TABLE 2 C Si Cr Ni Mo B V X5 1.7 3.5 16.0 16.0 2.0 3.5 0 DE 199 01 170A1 2.0-4.0 0.5-3.5 6.0-15 2.0-7.0 1.5-7.5 2.0-4.5 6.0-14.0For both alloys: the balance is Fe (in the case of X5 the Fe balance is57 wt %). The X5 alloy has a melting temperature of 1080° C. and lowhardness of 58 HRC.

Wear Test

In the ASTM G65 rubber wheel sand abrasion wear test the standard wearvalue of 13.68 mm³ loss was recorded after 2000 revolutions of thewheel. This resulting wear resistant value is at a similar to the wellestablished nickel-based wear resistant material called “12112”, sold byCastolin Eutectic. This 12112 alloy is a blend of a NiCrBSi 12496 alloymatrix with 35% WC, which has the following composition:

TABLE 3 Fe C Cr B Ni Si Mo Alloy 12496 3.88 0.78 14.8 3.13 73.31 4.1 0matrixThis Ni based 12112 alloy (=blend of alloy 12496 alloy with 35% WC) hasbeen sold for at least 20 years and have been used to make Fused powderplates, sold under the name of CP 112, by Castolin Eutectic.

The fact that the Alloy X5 achieved the same G65 wear resistance resultas the established 12112 is a surprise and a breakthrough, as the 12112needs to have 35% of expensive WC added to achieve this value and anexpensive Ni-based matrix. Alloy X5 is an Fe-based product and has no WCpresent.

Corrosion Tests

For corrosion tests specimens with near cylindrical shape were preparedby melting of the test material in ceramic crucibles and cut into slicedwith two exposed circular surfaces. The measurement of weight andsurface area was recorded.

The test material are the above mentioned Fe-based powder B (table 1)and Ni-powders A (table 1, No. 53606) as well as powders of standardNi-based alloys known as “12496” and “12497”(a slight chemicalmodification of alloy 12496). Said Ni-based powders were mixed with theFe-based powder B (table 1) at various mixing ratios.

The slice specimens were exposed to HCl (33%), HNO₃ (55%), H₂SO₄(96%)and acidic acid (80%) and the weight loss after 24 h, 48 h and 120 h wasmeasured. The corrosion resistance as specific weight loss (weight lossin mg per cm² and 24 h) was determined.

The diagram of FIG. 2 illustrates the corrosion test results of threetest series for different compositions exposed to HCl (33%). The threecurves are weight loss data points obtained from the corrosion tests asexplained above. The weight loss is plotted on the y-axis in [mg/(cm² xh)] in dependence of the fraction of the respective Ni-based A powder ofthe mixed powders for the preparation of the specimens.

The diagram of FIG. 3 illustrates the corrosion test results of threetest series for different alloys exposed to HNO₃ (55%). The three curvesare weight loss data points obtained from the corrosion tests asexplained above. The weight loss is plotted on the y-axis in[mg/(cm²×h)] in dependence of the content of the respective Ni-based Apowder of the mixed powders for the preparation of the specimens.

The results are as follows:

-   -   Ni-based alloys (A, 12496, 12497) show good corrosion resistance        against HCl. Fe-based do not (Powder B). With increasing content        of the Ni-based powder in the respective powder blends, the        corrosion resistance against HCl increases.    -   Fe-based alloy (B) shows good corrosion resistance against HNO₃.        With increasing content of the Fe-based powder in the respective        powder blends, the corrosion resistance against HNO₃ increases.    -   Ni and Fe-based alloys are resistant against acetic acid and        H₂SO₄.    -   Adding Ni-based powders (A, 12496, 12497) to Powder B improves        the corrosion resistance against HCl but decreases the        resistance against HNO₃. The best balance is achieved with a        Ni-based powder percentage of 5-15% as can be seen in FIGS. 2        and 3.

The optimum alloy blend of Ni-based powder into the Fe-based Powder Bcomposition is 15% (in wt % of the Ni-based powder) for HCl and HNO₃,with the use of Powder A as the best source of Ni-based alloy. This15%/85% mix gives the composition of X5 according to this preferredembodiment of the invention. This X5 composition also gives the lowestG65 wear resistance results.

1. A material comprising an alloy containing 13 to 16 percent by weightnickel (Ni), 13.5 to 16.5 percent by weight of chromium (Cr), 0.5 to 3percent by weight of molybdenum (Mo), 3.5 to 4.5 percent by weight ofsilicon (Si), 3.5 to 4 percent by weight of boron (B) and 1.5 to 2.1percent by weight of carbon (C), and a balance of the alloy comprisingiron (Fe).
 2. A material according to claim 1, wherein the alloycontains no elements other than Ni, Cr, Mo, Si, B, C and Fe, exceptimpurities.
 3. A material according to claim 1, wherein the alloy has acomposition of 13 to 14 percent by weight of nickel (Ni), 14 to 16percent by weight of chromium (Cr), 1 to 3 percent by weight ofmolybdenum (Mo), 3.5 to 4.5 percent by weight of silicon (Si), 3.5 to 4percent by weight of boron (B), 1.8 to 2.1 percent by weight of carbon(C) and 0.2 to 0.5 percent by weight of copper (Cu), and the balancebeing of iron (Fe).
 4. A material according to claim 1, wherein thealloy has a hardness of less than 60 HRC.
 5. A material according toclaim 1, wherein the alloy has a melting point of less than 1150° C. 6.A material according to claim 1, wherein the alloy is a powder or a wireor the alloy is a coating on a metal substrate.
 7. A material accordingto claim 1, wherein the alloy is free from preformed hard particles. 8.A material according to claim 1, wherein the alloy contains less than 1percent of weight of vanadium.
 9. A material according to claim 1,wherein the alloy is free of preformed particles of tungsten carbide.10. A material according to claim 1 wherein the alloy is free ofvanadium.